The present invention relates to a magnetic storage medium and, more particularly, a magnetic storage medium in which friction caused by bringing a head into slidable contact with the magnetic storage medium is decreased and a method of manufacturing the magnetic storage medium.
As a recording/reproducing method of a magnetic storing apparatus having constituent units constituted by a magnetic recording/reproducing head (to be referred to as a head hereinafter) and a magnetic storage medium, the following method is generally known. That is, after the head and the magnetic storage medium surface are set in a contact state at the start in an operation, the magnetic storage medium is rotated at a predetermined rotational speed to form a spacing corresponding an air layer between the head and the magnetic storage medium surface, and, in this state, a recording/reproducing operation is performed (contact.start.stop scheme; to be referred to as CSS hereinafter). According to this method, the rotation of the magnetic storage medium is stopped upon completion of the operation, and, at this time, the head and the magnetic storage medium surface are set in a contact friction state as at the start in the operation. A friction force generated between the head and the magnetic storage medium in the above contact friction state causes wear between the head and the magnetic storage medium, and the head and the magnetic body may be damaged at last. In addition, in the contact friction state, a small change in posture of the head makes a force acting on the head ununiform, and the head and the magnetic storage medium surface may be damaged.
According to a conventional technique, in order to prevent friction of the magnetic storage medium caused by slidable contact between the head and the magnetic storage medium, a graphite- or diamond-like carbon film as described in U.S. Pat. No. 4,277,540 or U.S. Pat. No. 4,411,963 or Japanese Patent Laid-Open No. 62-103823 or 53-143206, or a carbon film containing hydrogen atoms as described in Japanese Patent Laid-Open No. 64-37711 is coated as a protective film, and a lubricant such as a perfluoropolyether described in Japanese Patent Laid-Open No. 52-49805 is coated on the protective film. In this case, as the perfluoropolyether, one of perfluoropolyethers each consisting of a main chain (parenthesized part) and functional groups "G" and expressed by the following formulas is used.
Lubricant A: GCF.sub.2 (OCF.sub.2).sub.p (OC.sub.2 F.sub.4).sub.q OCF.sub.2 G PA1 Lubricant B: F(C.sub.3 F.sub.6 O).sub.n C.sub.2 F.sub.4 G PA1 Lubricant C: F(CF(CF.sub.3)CF.sub.2 O).sub.m CF.sub.2 G
(wherein p and q are integers of 2 to 25, and G is a functional group such as --COOH or --OH.) PA2 (wherein n is an integer of 3 to 25, and G is a functional group such as --COOH or --OH.) PA2 (wherein m is an integer of 3 to 25, and G is a functional group such as --COOH or --OH.)
However, the above carbon film does not have, on its surface, adsorption sites for adsorbing a lubricant, and the lubricant consisting of a perfluoropolyether is only coated on a protective film constituted by the carbon film. For this reason, the lubricant has poor adhesion properties to the protective film constituted by the carbon film, and the lubricant is gradually peeled in a CSS test. The protective film is worn to smooth the protective film surface, and a friction force increases, thereby degrading mechanical durability. This is because the surface of a carbon film formed by plasma chemical vapor deposition (CVD) or sputtering is stabilized by a graphite structure or double bonds. In addition, even when the graphite layer on the surface is mechanically removed by abrasion or the like, and adsorption sites such as dangling bonds are formed on the surface, although the dangling bonds are unstable in the air, the dangling bonds are oxidized or adsorb water so that the dangling bonds are stabilized within a short time (about several milliseconds). A dangling bond is defined as a chemical bond associated with an atom in the surface layer of a solid that does not join the atom with a second atom but extends in the direction of the solid's exterior. For example, according to description in Japanese Patent Laid-Open No. 64-37711, the dangling bonds of carbon atoms of a carbon film are eliminated by adding hydrogen atoms so as to stabilize the carbon film, and the adhesion properties of the carbon film to a ferromagnetic metal thin-film layer is improved. However, when the protective film is stabilized, the adhesion properties of the protective film to the ferromagnetic metal thin-film layer or a lubricant become poor, and mechanical durability is unexpectedly degraded.